Electrical resistance element



Patented Feb. 2, 1943 UNITED STATES PATENT OFFICE ELECTRICAL RESISTANCE ELEMENT William Kroll, Luxemburg, Luxemburr: vested in the Alien Property Custodian No Drawing. Original application January 17,

1940, Serial No. 314,229. Divided and this application March 8,1940. Serial No. 322,930. In Luxembnrg July 24, 1939 2 Claims. I (Cl. 201-76) peratures.

It is known that electrolytically refined gamma manganese remains in that state for severalweeks, and that during such time itmay be cold-worked. But in time the gamma manganese alters to the brittle alpha form, and it has heretofore been impossible to obtain by thermal treatment forms of manganese or high-manganese alloys that are stably ductile at room temperatures.

I have observed that pure manganese obtained by distillation may be hot rolled at temperatures above the alpha-beta transformation point,

the best results being obtained in the neighbor-- ment is employed, the resulting alloys may be kept in a ductile condition at room temperature. The invention is further based on the discovery that electrical resistance elements made of manganese-copper alloy and manganese-copper nickel alloys have a high electrical resistivity.

The alloying addition producing the most favorable results is copper' in a proportion of about 1% to 60%, preferably between and 35%, of the alloy and nickel in a proportion of about 0.5% to 25% of the alloy. I

In order to obtain the maximum freedom from brittleness, it is important .when making the alloys to protect the molten metalfrom the nitrogen and oxygen of the air. This may be done by the use of protective fluxes, e. g. slags containing manganese chloride, manganese oxide and alkaline earth metal halides; or by the use of a protective atmosphere, for instance hydrogen. methane, and the rare permanent gases such as argon or helium; or by the use of a partial vacuum, if it be not carried to such a point as to vaporize'manganese too rapidly; or

. by a combination of two or three of these measures. Clay crucibles may be used in preparing the alloy.

The hot rolling of the alloys of the invention must be conducted entirely above the beta-alpha transformation temperature, and preferably is commenced while the alloy is in the gamma form. Otherwise, the metal tends to beredshort or cold-short. The beta-alpha point is about 740 C. in the case of the manganesecopper alloys. .Further alloying additions may change the transformation point upwards or downwards.

Moreover, the cast ingots (particularly heavy sections) should not be permitted to cool below the beta-alpha transformation temperature before rolling. While the brittle as-cast structure is still present, cooling to room temperature and reheating to rolling temperature will cause cracks and red-shortness.

According to the invention, the cast ingots, still hot, are hot rolled in the gamma-beta re,- gions until the grain has been broken down. The thinner cross sections may then be rapidly cooled, thereby avoiding embrittlement. Thus, for example, ingots mm. of a manganese alloy containing 15% or more copper are rolled at 950 C. into sheets 2 mm. thick which may then be air cooled.

Cold working may be done within wide limits, intermediate anneals being effected by rapid heating to within the beta or gamma field, followed by quenching.

Although binary manganese-copper alloys are relatively stable, theynevertheless tend to bee come brittle when heated to certain moderately ample, an alloy containing 6.9% Ni, 5.1% cu,

rest Mn, is substantially entirely stable, and

after working and quenching from 950 C. has

a tensile strength of 39.9 kg./mm. with 20% elongation and a Brinell hardness of 105. In

general, the alloys containing the higher percentages of copper tolerate the higher nickel additions.

Aluminum, suitably in an amount between 0.1% and serves to deoxidize the alloys, thereby improving their workability. Further- .more, aluminum protects the alloy against oxidation at high temperatures and during melting and casting it forms a superficial film of oxide which hinders oxidation and nitrogen pick-up. It promotes the existence of a surface favorable for rolling. The aluminum-containing alloys may advantageously be made from manganese produced by alumino-thermic reduction.

Zinc may also be added in a proportion up to the copper preferably being correspondingly reduced. A more narrowly circumscribed limit for such alloys is between 5% and copper and 1% to 8% zinc. For instance, an alloy containing 10% Cu, 5% Zn, rest Mn, after rolling and quenching from 1050 C. and subsequent cold working, had a tensile strength of 47.7 kg./mm. with 13.1% elongation and a Brinell hardness of 131.

Other metals may be present, as one or more of iron, cobalt, tungsten, or chromium, in a total percentage up to 5% but preferably not over about2%. In general, the elements Si, Sn, Ti, Ta, Mo, Ag, Ce, Mg, and Be appear to be injurious and should ordinarily not exceed 0.5% Si, 1% Sn, 2% Ti, 5% Ta, 2% Mo, 2% Ag, 2% Ce. 1% Mg, or 0.5% Be. Calcium, lithium, or thorium may be used in a proportion of 1% or more as a deoxidizer. The alloys containing the higher percentages of copper or of copper and nickel will tolerate the higher amounts of such other-metals. It is preferred that the silicon content be less than 0.15%. e

The alloys of the invention preferably contain less than 0.2% carbon and should usually contain less than 0.05% of this element, although somewhat higher carbon contents will on occasion bepermissible. It is also preferred that the manganese content be at least although on occasion it may be as low as 40%.

The resistance of the alloys of the invention to corrosion by moist air is about the same as that of pure copper. Scaling accompanied by peeling is noticeable only above 600 C. in the case of the lower copper alloys and only above 700 C. in the case of the higher copper alloys.

The alloys containing over 30% copper may easily be soldered with either soft or hard solder. Those with less than 30% copper are soldered with some difliculty.

The alloys of the invention have a particularly high electrical resistivity. generally between about and 200 microhms/cm}. For example, an alloy containing about 37% copper, 8% nickel, rest manganese, has an electrical resistivity of about 180 microhms/omit three times that of commercial resistance-wires of copper-base alloys; while an alloy containing 5% copper, 8% nickel, rest manganese, has a resistivity of microhms/cm.

The highest resistivities are obtained in the range of 30% to 55% copper, and the addition of 6% to 8% nickel is suflicient to stabilize the alloy. If the alloy is to be used at temperatures below 100 C., the nickel content may be as low as 0.5% or be eliminated entirely. If desired, the nickel content may be raised as high as 20%. Nickel only slightly affects the resistivity, the latter being determined chiefly by the solid solution of manganese and copper.

Within the range of 25% to 55% copper, 0% to 15% nickel, rest manganese, the temperature coefficient of electrical resistivity is low, e. g. alpha==0.0003 for an alloy containing 50% manganese and 50% copper. The higher-manganese alloys have a relatively high temperature coefllcient, for instance, alpha=0.03 for an alloy containing 95% manganese and 5% copper. Nickel does not have any pronounced effect on the temperature coefilcient of electrical resistivity.

It is to be understood that the several specific compositions described herein are examples illustrative of the invention, and that the invention is not limited to or by such examples.

I claim:

1. Electrical resistor element composed of an alloy consisting of manganese, copper, and nickel, the manganese content being upwards of 50%, the nickel content being at least 0.5% but less than 10%, and the copper content being the remainder and amounting toat least 15%, said alloy element being in the ductile condition resulting from quenching it from a temperature above the beta-alpha transformation point at about 740 C.

2. Electrical resistor element as claimed in claim 3, composed of an alloy wherein the nickel content is between 2% and 8% and the copper content is at least 30%, said alloy element being in the ductile condition resulting from quenching it from a temperature above the beta-alpha transformation point at about 740 C. and said element having a specific electrical resistance above microhms per centimeter cube.

WILLIAM KROLL. 

